Method for producing a filament yarn with alternating S- and Z-twists

ABSTRACT

A method for producing a filament yarn with alternating S- and Z-twists. The yarn is moved between two twisting stops and submitted alternatively to S- and Z-twisting by at least one false twisting unit. The twists are fixed in a fixing unit situated downstream from the false twisting unit. The twisting stop downstream of the fixing unit is moved synchronously with the yarn and held in a yarn engagement position to stop the twisting until at least the twisting inversion points is fixed in the yarn. At least one other twisting stop oriented at a distance from the above mentioned moving twisting stop is engaged with the yarn in a way to stop the twisting and is moved along with the yarn before said yarn is submitted to an opposite twisting by the false twisting unit.

FIELD OF THE INVENTION

The invention relates to a method for producing a filament yarn withalternating S- and Z-twists, in which at least one yarn is moved betweentwo spaced apart twisting stops arranged at a distance from each other,and the yarn receives thereby through at least one false twisting unitof the clamping type arranged between the twisting stops alternately S-and Z-twists which are fixed by means of a fixing unit which isinterconnected downstream of the false twisting unit in yarn advancingdirection.

BACKGROUND OF THE INVENTION

In such a method known from the DE 39 31 110 C2, the twisting stops areformed by two stationarily arranged delivery mechanisms, of which one isarranged upstream of the false twisting unit or units, and the other onedownstream of the fixing unit, which is designed either as a heatingdevice or as an air-circulating device. The alternating formation of theS- and Z-twists is carried out in a predetermined cycle by switching onand off the clamping action of the false twisting unit. Since, however,the second twisting stop is arranged downstream of the fixing unit inyarn advancing direction, the S- and Z-twists earlier applied to theyarn are, depending on the twisting direction, partially again untwistedand partially yet more tightly twisted in the yarn section extendingdownstream of the false twisting unit. Thus it is not possible in thismanner to produce a yarn which has reproducible alternately defined S-and Z-twists. Furthermore nontwisted sections with a lesser S- orZ-twist are each created between the sections with S-twist and thesections with Z-twist.

SUMMARY OF THE INVENTION

The basic purpose of the invention is therefore to provide a method forproducing a filament yarn with alternating S- and Z-twists, with whichin a simple, economical and reproducible manner a filament yarn can beproduced which has defined S- and Z-twists per unit of length andtherebetween as much as possible no nontwisted or little twistedsections.

This is attained according to the invention by the twisting stopprovided in yarn advancing direction downstream of the false twistingunit being moved synchronously with the yarn and being held in anengagement with the yarn stopping the twisting until at least thetwisting inversion point in the yarn is fixed, and by at least onefurther twisting stop, following the aforementioned moved twisting stopat a distance, entering into an engagement with the yarn stopping thetwisting, and advancing together with same before the yarn is twisted inan opposite direction by the false twisting unit.

Thus the invention is based on the thinking to grasp the yarn directlybehind the false twisting unit by twisting stops successive in timelyand spacial intervals, and to then advance the twisting stopssynchronously together with the yarn. A twisting stop has the purpose toprevent a continuation of a twist applied to the yarn into a yarnsection lying upstream of or downstream of the twisting stop. Clampingdevices are primarily used as twisting stops in the present case,however, a twisting stop can also be designed as a guide edge or throughclamping in a delivery mechanism. Yarn sections are in the inventivemethod each temporarily “fixed” between two spaced twisting stops whichfollow each other until the final fixation by means of the fixing unittakes place. The yarn sections extending fixed between two twistingstops have either a S- or Z-twist with a specific twist, whereby theterm “twist” means according to DIN 60900, Part 2, the number of twistsof a single yarn per/m. The specific twist of a section of yarn clampedbetween two adjacent twisting stops is not influenced or changed by thetwists applied to the following yarn sections because the false wire isconstructed always only up to the twisting stop closest to the falsetwisting unit. In this manner also nontwisted sections between the yarnsections with S- or Z-twist are avoided. The inventive method can becontinuously carried out and enables the production of a filament yarnwith alternating S- and Z-twists. The filament yarn can be produced outof a yarn component, namely a bunch of filaments, and is fixed duringthe production process following the false twisting unit, which is doneby thermofixation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be discussed hereinafter in greater detail inconnection with the exemplary embodiments illustrated in the drawing, inwhich:

FIG. 1 schematically illustrates the structure of the finished filamentyarn,

FIG. 2 schematically illustrates the operating sequence for the method,

FIG. 3 illustrates the relationship between the minimal distance of themovable twisting stops from the false twisting unit under thetheoretical twist distribution,

FIGS. 4a to 4 c illustrate the operating principle of twoseries-connected false twisting units in a first embodiment,

FIGS. 4d to 4 f illustrate the operating principle of a secondembodiment,

FIGS. 5 to 7 schematically illustrate various movable twisting stopdevices,

FIG. 8 is a view in direction VIII of FIG. 7.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates the structure of the finished filamentyarn. Same has alternating yarn sections 1 a with S-twists and yarnsections 1 b with Z-twists. The twisting inversion points 2, theexpansion of which in longitudinal direction of the yarn can be keptvery small with the inventive method, each lie between two yarn sections1 a, 1 b with opposite twists. The lengths of the yarn sections 1 a , 1b can vary. Smooth and textured multi-filament yarns, preferably in atiter range of between 17 and 330 dtex, are supposed to be utilized asfeed materials. FIG. 2 schematically illustrates the operating sequencefor the method. The yarn 1′ is moved from A to B in a yarn advancingdirection C by means of the delivery mechanism 6, and leaves thedelivery mechanism 6 as a finished filament yarn 1 with alternating S-and Z-twists, as it is illustrated in FIG. 1. A first twisting stop 7 isarranged stationarily and can advantageously be designed as a deliverymechanism or as a yarn tensioning device. A false twisting unit 8 isarranged at a distance L₀ downstream of the stationary twisting stop 7,with which false twisting unit it is possible to subject the yarn 1′successively to alternating S-twists and Z-twists. The detailed designof such false twisting units 8 will be discussed later on in connectionwith FIGS. 4a to 4 f. A twisting stop device 9 with several twistingstops 3 movable in the yarn advancing direction C is provided behind thefalse twisting unit 8. Each twisting stop 3 is formed by two cooperatingclamping jaws 3 a, 3 b, whereby these clamping jaws 3 a, 3 b aresupposed to have an as small as possible expansion in the yarn advancingdirection C, and are therefore advantageously designed like a blade. Itis thus possible to reduce the length expansion of the twistinginversion point 2 to a minimum so that in the finished textile surfacethese inversion points 2 do not appear as areas of error. The clampingjaws 3 a, 3 b are arranged on continuously driven belts 10 a, 10 b, withwhich they each can be returned to the false twisting unit 8.Furthermore the clamping jaws 3 a, 3 b can in this manner be turned onand off. In the area lying between the belts 10 a and 10 b, opposingpairs of clamping jaws 3 a, 3 b are pressed against one another with theinter positioning of the yarn 1′ to form then a twisting stop 3 movablein the yarn advancing direction C. The movable twisting stops 3 arespaced apart at a distance L₂. The twisting stops 3 are moved through afixing unit 11, which consists of a heating zone 4 and a downstreamoriented cooling zone 5. The spaced apart distance L₂ of the twistingstop 3 is thereby less than the length L₃ of the fixing unit 11. It isassured in this manner that the twists alternately oppositely applied tothe yarn 1′ and temporarily fixed between two twisting stops 3 arethermally fixed when the finished filament yarn 1 leaves the fixing unit11.

In order for the method to operate as effectively as possible, thetwisting stops 3 should engage the yarn 1′ to stop the twisting as closeas possible to the false twisting unit 8, and should then be advancedsynchronously with the yarn 1′. With each new engagement of the yarn bya twisting stop it is possible to change the direction of the twistapplications through the false twisting unit 8. Yarn sections 1 a withS-twist and yarn sections 1 b with Z-twist are alternately temporarily“fixed” between two twisting stop devices, and the yarn 1′ is moved in atwisted state initially through the heating zone 4 and then through thecooling zone 5. Only after the yarn has been cooled off to below aspecified temperature, the clamping is cancelled during an exit from thecooling zone 5. Because of the varying distance L₀ between thestationary twisting stop 7 and the false twisting unit 8 on the one handand the distance L₁ between the false twisting unit 8 and the movabletwisting stop 3 closest to it on the other hand, varying twist heightsare created, namely twists per unit of length, in front of and after thefalse twisting unit 8. However, only the portion of the twists which liebetween the false twisting unit 8 and the nearest moved twisting stop isfixed in the production process. The yarn is theoretically only tightlyuntwisted and tightly twisted in the area between the twisting stop 7and the false twisting unit 8. The false twist is thus divided into twoopposite true twists, of which in each case only the twist downstream ofthe false twisting unit is fixed. In order for this twist to no longerbe influenced by the following reversal of the twisting direction, thistwisting direction is supposed to be reversed only when the followingtwisting stop engages the yarn 1′. The respective next twisting stop ishereby supposed to be guided close to the false twisting unit 8 in orderto keep the distance L₁ as small as possible. Namely, the yarn sectionin the area L₁ must during a reversal of the twisting direction be firstagain untwisted and twisted in the opposite direction. The shorter thedistance at the start of the reversal of the twisting direction, themore effectively operates the method.

This can be recognized by looking at FIG. 3, which shows the theoreticalinfluence of the distances L₀ and L₁ on the twist height upstream of anddownstream of the false twisting unit 8. The times for the engagementsof the movable twisting stops are indicated by the reference 3′. FIG. 3illustrates that a large relationship of L₀/L₁ has a positive effect,and that the minimal distance L₁ between the respective twisting stop 3which engage the yarn 1 and the twisting unit 8 should be as small aspossible.

The changing twisting direction of the yarn can be realized both by onefalse twisting unit with changing twisting direction and also by twofalse twisting units which are constantly driven in opposite twistingdirections, and which can be alternately interconnected. The use of twofalse twisting units, which are driven in different twisting directionsand the active surfaces of which are interconnected, is advantageous.The masses, which are to be accelerated, are in this manner kept verysmall since the respective interconnection can occur through a movementof the yarn or through a deflection of the active areas.

False twisting units 8, 8′ or 8 a, 8′a of the clamping type areillustrated in FIGS. 4a to 4 f. In the exemplary embodiment illustratedin FIGS. 4a to 4 c, each of the false twisting units 8, 8 a has twocrossing, continuous belts 12, 12′, at the crossing point of which theyarn 1′ can be clamped in order to create the twists. The belts 12 ofthe first false twisting unit 8 are, for example, driven in such amanner that they can give the yarn downstream, namely in yarn advancingdirection downstream of the false twisting unit a S-twist, whereas thebelts 12′ of the second false twisting unit 8′ can give the yarndownstream of the false twisting unit 8′ a Z-twist. Each of the twofalse twisting units 8, 8′ has furthermore two pressure rollers 13, 13′,respectively, with the help of which the active areas 12 a, 12′a of thebelts 12, 12′, respectively, which are usually spaced from the yarn 1′,can be alternately moved into operating position, as this is illustratedin FIGS. 4b and 4 c. The belts 12, 12′ of the two respective falsetwisting units 8, 8′ are continuously driven in the twisting directionsindicated by arrows. When according to FIG. 4b the pressure rollers 13press the active areas 12 a against the yarn 1′, the yarn receivesS-twists downstream when the second false twisting unit 8′ becomesinactive. In order to give the yarn Z-twists downstream, the pressurerollers 13 of the first false twisting unit 8 are according to FIG. 4cmoved away from one another and the pressure rollers 13′ of the secondfalse twisting unit 8′ press the active areas 12′a against the yarn 1′.By deflecting the active areas 12 a, 12′a of the belts 12, 12′perpendicular to their direction of movement, very quick switchingoperations can be realized since, due to the geometry, only very smallforces must be applied and only short paths of movement must be covered.The false twisting unit, which is not in the operating position, doesnot hinder the expansion of the twists in the yarn 1′ since their activeareas 12 a or 12 a ′ are each spaced from the yarn 1′.

Each of the two false twisting units 8 a, 8′a consist in the exemplaryembodiment illustrated in FIGS. 4d to 4 f of two continuously drivendisks 14, 14′, the axial faces of which form the active areas 15, 15′,between which the yarn 1′ can be clamped. This is accomplished by thetwo disks 14 or 14′ axially approaching one another. Thus it ispossible, for example according to FIG. 4a, to give the yarn 1′downstream, namely in yarn advancing direction C the yarn sectionextending downstream of the false twisting unit 8 a, Z-twists when theactive areas 15 of the disks 14 are pressed against the yarn 1′ and theactive areas 15′ of the second false twisting unit 8 a ′ are spaced fromthe yarn 1′ and are thus inactive. The active areas 15′ are in theposition of the false twisting units illustrated in FIG. 4f pressedagainst the yarn 1′ and the yarn thus receives downstream S-twists andthe first false twisting unit 8 a is inactive.

Various twisting stop devices are illustrated in FIGS. 5 to 7. Thetwisting stop device 9 illustrated in FIG. 5 corresponds essentially tothe exemplary embodiment illustrated in FIG. 2 so that an explanationreference can be made to the description of FIG. 2. The evenly drivencontinuous driving means 10 a, 10 b, can, for example, be belts orchains.

Several rigid clamping elements 17 are, in the twisting stop device 9′illustrated in FIG. 6, arranged spaced from one another on thecontinuous driving means 16. A movable clamping element 18, which ispivotal about an axis 19, is associated with each rigid clamping element17. When the movable clamping element 18 is pressed against the rigidclamping element 17, clamping occurs. A control cam 20 can be used tocontrol the movable clamping element 18. The heating zone is identifiedby the referenced numeral 4.

Several support arms 21 are provided, in the twisting stop device 9″illustrated in FIG. 7, spaced from one another on a continuous drivingmeans 16, which support arms each carry one rigid clamping jaw 22 ontheir free end. Each support arm 21 is associated with a movable slidemember 23 having a clamping jaw 23 a. The slide members 23 can be movedrelative to the support arms 21 in their longitudinal direction byoperation of a control cam 20 or the like, and the movable clamping jaws23 a can thus each be moved into a clamping position or an openingposition. Each clamping jaw pair 22, 23 a forms one twisting stop.

In the exemplary embodiment illustrated in FIGS. 7 and 8, the clampingjaws 22 are arranged on relatively thin support arms 21 and at a greaterdistance from the driving means 16. When the clamping jaws 22, 23 a arein a clamping position and thus in an engagement to stop twisting, theycan elastically yield in yarn-advancing direction C and can thuscompensate for changes in the length of the yarn, which changes can becreated by twisting and shrinkage.

When the fixing unit 11 consists of a heating zone 4 and a cooling zone5 connected thereafter, each yarn section 1 a , 1 b including theinversion points 2 lying therebetween is fixed. If necessary, it is,however, also possible to fix only the inversion points 2, which can,for example, be accomplished by heated clamping jaws.

What is claimed is:
 1. In a method for producing a filament yarn withalternating S- and Z-twists comprising the steps of: clamping at leastone yarn at two spaced apart twisting stops, applying through at leastone false twisting unit stationarily arranged between the twisting stopsalternately S- and Z-twists, and fixing the twists by means of athermo-fixing unit positioned downstream of the false twisting unit inyarn advancing direction, wherein the improvement comprises the steps ofbringing the first of said two twisting stops arranged downstream of thefalse twisting unit in clamping engagement with the yarn, therebystopping the twisting at the clamped location; advancing synchronouslysaid first twisting stop and the yarn clamped thereto through the fixingunit, until at least the twisting inversion point in the yarn is fixed;bringing at least one further twisting stop following the aforementionedfirst twisting stop into clamping engagement with the yarn, therebystopping the twisting at the clamped location; and advancing saidfurther twisting stop and the yarn clamped thereto through the fixingunit, before the yarn is twisted in an opposite direction by the falsetwisting unit.
 2. The method according to claim 1, wherein a length ofthe fixing unit has a series oriented heating zone and a cooling zone,and orienting the spacing between the moved twisting stops to a spacingwhich is smaller than the length of the fixing unit.
 3. The methodaccording to claim 1, wherein the clamping of the yarn by the firsttwisting stop is released as soon as the yarn in the cooling zone fallsbelow a certain temperature.
 4. The method according to claim 1, whereinthe first and further twisting stops are moved linearly.
 5. The methodaccording to claim 4, wherein the location whereat clamping is occurringby the first and further twisting stops is controlled to be as small aspossible of a dimension in the yarn advancing direction.
 6. The methodaccording to claim 5, wherein said small as possible dimension iscontrolled by providing bladelike clamping jaws.
 7. The method accordingto claim 1, wherein said clamping occurs in each instance by moving apair of jaws toward one another.
 8. The method according to claim 1,wherein the movable twisting stops are cyclically returned to an initialposition adjacent the false twisting unit.
 9. The method according toclaim 8, wherein each respective first and further twisting stop isfirst guided close to the false twisting unit prior to entering into theclamping engagement with the yarn.
 10. The method according to claim 1,wherein the in-between distance between two of the moving twistingstops, which are in clamping engagement with the yarn to stop twisting,is elastically flexible in yarn advancing direction.
 11. The methodaccording to claim 1, including a controlling of the distance betweenthe twisting stop stationarily arranged upstream of the false twistingunit and the false twisting unit to be at any time greater than thedistance between the false twisting unit and the movable twisting stopwhich is the closest to said false twisting unit.
 12. The methodaccording to claim 1, wherein the movable twisting stops are moved withthe yarn through the thermal fixing unit having a series orientedheating zone and a cooling zone interconnected thereafter.
 13. Themethod according to claim 1, wherein the moving twisting stops areheated in order to fix the twistings of the yarn.
 14. The methodaccording to claim 1, wherein the false twisting unit includes twoconstantly driven false twisting units of which one is suited to givethe yarn downstream S-twists and the other is suited to give the yarnZ-twists, and wherein the false twisting units are moved alternatelyinto an operating yarn engaging position.
 15. The method according toclaim 1, including a controlling of the time of the twist applicationsin the respective direction so as to correspond with the length of theyarn section with one twisting direction.
 16. The method according toclaim 1, wherein the distance between two twisting stops isstochastically changed.
 17. The method according to claim 1, includingan urging of opposing pairs of the movable twisting stopsforce-lockingly together to effect the clamping of the yarntherebetween.